A speaker system may include a collection of individual loudspeakers in an array, a line, or a co-planar arrangement. Individual loudspeakers in a speaker system may use one or more types of various speaker designs, such as moving-coil speakers, piezoelectric speakers, and electrostatic speakers. Many conventional speakers are relatively large and less likely to meet the increasing demands for lightweight, thin, or small electronic devices. To make speakers more portable, planar or flexible speakers have been developed. As another example, piezoelectric speakers may be made flexible by employing light, flexible membrane materials, such as polyvinylidene fluoride (PVDF) films.
One of the characteristics considered in evaluating a loudspeaker or a speaker system is directivity, which may be measured by sensing the sound pressures of sounds radiated from a speaker or speaker array to various directions. In a loudspeaker system, an increased directivity may be implemented in certain applications, so that the sound energy or wave is radiated in toward a certain direction or toward a narrower area. Increased directivity may prevent howling or other effects that may affect the characteristics of the sound heard by a listener.
A number of approaches were employed to provide better directivity of speakers. As an example, steering technology may be applied to control the phase or phases of audio signals. As another example, ultrasonic transducers may be employed in parametric audio systems for generating sonic or ultrasonic signals in nonlinear transmission media. Specifically, a parametric audio system, which is generally directional, may include components such as an amplitude modulator, driver amplifier, and an ultrasound transducer array. The amplitude modulator may modulate signals so that audio waves may be carried within the ultrasound wave, thereby using the ultrasound wave as a carrier to carry the audio waves to a pointed direction. One or more driver amplifiers may be used amplify the modulated signal, and an ultrasound transducer array having ultrasonic transducers may be used to generate ultrasound waves and send through the air along a selected path of projection.
Because of the non-linear propagation responses of the air to sound waves, the modulated signals or waves may demodulated as it passes through the air, thereby regenerating the carried sound wave along the selected path. The transducer in a parametric audio system may be driven by the driver amplifier, which may require a high voltage signal in hundreds of volts. The use of high voltage connections between the driver amplifiers and the transducers may increase the size and cost of the system in some examples.
Therefore, it may be desirable in some applications to provide a speaker array that may be directional or may be flexible in its directivity characteristics.